The present invention relates to the use of fuzzy logic integrated intelligent control to improve the efficiency of electric motors.
It is estimated that over 60 percent of the electricity generated in the U.S. is consumed by electric motors. Since the principal energy source for the generation of electricity in the United States and worldwide is through use of the combustion of fossil fuels, a reduction of electric power consumption can result in a significant decrease in the combustion of fossil fuels and a significant reduction in the release into the atmosphere of sulfur dioxide (SO.sub.2) and carbon dioxide (CO.sub.2), major atmospheric pollutants resulting from such combustion. It is believed that SO.sub.2 and nitrogen oxides (NO.sub.x), contribute to acid rain and CO.sub.2 contributes to the greenhouse effect and potential global climate change. A reduction in these emissions can improve air quality and decrease the environmental damage to lakes, rivers, and trees. Increasing the efficiency of electric motors will also reduce the cost of the end-use processes driven by the electric motors which can in turn lead to the reduction in the cost of manufacturing goods and providing services. Thus, reductions in the use of electric power can result in significant economic savings and environmental improvements.
Conventional motor controls are primarily directed at varying the motor speed to match the varying load requirements through the use of an adjustable speed drive (ASD). However, varying the speed of an electric motor to match or meet the load-requirements does not necessarily operate the motor at maximum power efficiency. Load/speed motor control with superimposed efficiency control is difficult to accomplish. Moreover, it is desirable to be able to readily modify or retrofit existing motors with a control arrangement which will provide, or improve, power efficiency. One reason that conventional electric motor speed control systems do not necessarily optimize power efficiency considerations is the control complexity of meeting all of the potential contradictory demands placed upon, and the large number of variables occurring within, such a system.
The present invention utilizes the inherent capabilities of fuzzy logic set theory in an integrated intelligent controller to improve the energy or power efficiency of electric motors, particularly alternating current (AC) induction motors, while at the same time meeting the demands of the process equipment and load operations which are driven by such electric motors. Fuzzy logic has the proven ability to represent complex, ill-defined systems that are difficult or impractical to model and control by conventional methods. In addition, fuzzy logic is a form of artificial intelligence theory which is possible to be implemented in an integrated electronic circuit device or microchip. This ability is important in the case of the modification, or retrofitting, of existing electric motors and related industrial systems, since microchips can be readily added through an add-on circuit board to existing controllers and require little additional electric power for their operation.
The theory of fuzzy logic and an explanation of its ability to be utilized in complex, ill-defined systems, is set forth, for example, in "Designing with Fuzzy Logic" by Kevin Self, pp. 42, IEEE Spectrum, November 1990, which article is hereby incorporated by reference. Fuzzy logic has been applied to various complex control systems. Examples include the use of fuzzy logic for determining a target value for the drive torque of a vehicle as set forth in U.S. Pat. No. 5,021,958. U.S. Pat. No. 4,809,175 describes the use of fuzzy logic in a vehicle for the control of speed and other parameters of an internal combustion engine. In Japanese patent JP3-18,397 the voltage and rotational speed of a motor are applied to a fuzzy logic processor in order to prevent an overload of the motor.
There is, thus, a long-standing need to improve the efficiency of electric motors, particularly large industrial motors, through a control system which is relatively inexpensive and capable of addition to existing industrial electric motors and processes through retrofitting, and yet which is equally applicable for incorporation into the design of new motor control systems.